The present invention relates to a polishing apparatus, a polishing member and a method of polishing an object such as a semiconductor wafer by using polishing cloth or the like.
Of the processes for producing a semiconductor element on a semiconductor wafer (hereinafter called a "wafer"), there is known a polishing process called CMP (Chemical Mechanical Polishing). According to this CMP process, a polishing liquid including mechanical polishing particles, and a chemical polishing agent or liquid is dropped onto a surface of the polishing cloth, and the surface of the polishing cloth is directly pressed on an object such as a wafer or a layer (an insulation layer or conductive layer) formed on the wafer. Then, part of the surface of the object is removed by the polishing treatment.
For example, a process of polishing the insulation layer is applied to a planarization step called the etch-back in a process of forming a multilayer interconnection.
According to a conventional CMP process, for example, in a CMP apparatus shown in FIG. 6, a surface of a wafer 10 or a layer formed thereon, held by a wafer holding mechanism 13 is pressed at a predetermined pressure on a rotary table 12 having a surface attached with polishing cloth 11 as a polishing layer. The rotary table 12 is rotated and also the wafer holding mechanism 13 is rotated by a motor 15 in directions shown by arrows while supplying a polishing liquid from a nozzle 14 to the surface of the polishing cloth 11. Thus, the surface of the wafer 10 (or a layer formed on the wafer) is polished by rotating and relatively revolving the wafer 10 on the rotary table 12.
Foaming resin such as foam urethane resin being, for example, about 1.2 mm thick is used as the polishing cloth 11, and a slurry liquid obtained by dispersing silica (SiO.sub.2) as mechanical polishing particles and the chemical polishing liquid is used as the polishing liquid. In this CMP process, mechanical polishing particles enter many recess portions formed by foaming on the upper surface of the foaming resin, and friction caused by the mechanical polishing particles captured in the recess portions, i.e. the mechanical polishing effect, can be thereby obtained. It is thought that the complex effect of both the mechanical polishing effect and the chemical polishing effect may be related greatly to the polishing mechanism.
In the above-described CMP process, for example, the polishing rate becomes lower every time one wafer 10 is polished. The reason can be understood as follows. When the wafer 10 is polished, shavings of the wafer 10 or layer formed thereon may enter the recess portions on the surface of the polishing cloth 11, as well as the mechanical polishing particles in the polishing liquid. When the polishing step proceeds and the shavings of the wafer 10 entering the recess portions are increased, the shavings may cause the mechanical polishing particles, which have entered the recess portions, to be taken out thereof.
Thus, as the polishing process proceeds, the mechanical polishing particles captured in the recess portions may be reduced, and proportionally to this, sliding between the polishing cloth 11 and the wafer 10 may become remarkable. Therefore, since a large friction force cannot be obtained, the polishing rate may become smaller.
At this time, since the shavings entering the recess portions on the surface of the polishing cloth 11 cannot be removed by a brush, etc., for example, the surface of the polishing cloth 11 is shaved by diamond, etc. to make a new surface of the polishing cloth every time one wafer 10 is treated. In order to execute this work, the polishing has to be interrupted. If this work is further executed, the foaming resin (polishing cloth 11) itself is also shaved, which causes the life cycle of the polishing cloth 11 to be shortened. For this reason, the polishing cloth 11 has to be replaced with a new one, for example, after processing five hundred wafers 10. Therefore, the troublesome exchange of the wafers has to be executed many times, and every exchange interrupts the CMP process. As a result, the throughput of the CMP process is lowered.